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Two MOFs are showing a low-energy solid-state transformation and a dissolution–recrystallization structural transformation respectively. The hydrogen uptake was found to be influenced by the polycatenation present in one of the frameworks.

Metal–organic frameworks with suitable voids are promising materials for their exceptional functionalities. With the incorporation of proper voids and modulation of structural flexibility, such fra...

To overcome the environmental issues arising from the burning of fossil fuel, an alternative effective source of energy is required. Hydrogen energy is one such alternative which can pave the purpose of interest. For a successive replacement of fossil fuel by hydrogen energy, hydrogen storing, especially in a vehicular system, is highly required and it is still a major challenge. A wide range of materials have been used for hydrogen storing. Metal-organic framework is one of them, which have been studied extensively both from academic and industrial viewpoint. These studies show that several metal-organic frameworks (MOFs) have excellent physisorption ability but normally at a very low temperature. To improve this at ambient conditions, various strategies have been introduced so far for MOFs, although an important aspect of external stimuli-responsive flexible or dynamic frameworks, have not been studied systematically. There are various advantages of the use of dynamic MOFs for hydrogen physisorption and sometimes helpful to overcome socio-economical barrier connected to this alternative energy source. In this highlight, prior strategies to improve hydrogen storage in MOF with special importance on external stimuli-responsive flexible MOF and their perspective importance in hydrogen storage have been discussed.

Interpenetration or catenation is well explored in the network structure of metal organic frameworks, but these kinds of networks were considered as not usable for normal applications of convention...

Five new azo-functionalized coordination polymers, namely {[Cd(3,3′-azbpy)(suc)]·(MeOH)}n (1), [Cd(3,3′-azbpy)(msuc)]n (2), {[Cd(3,3′-azbpy)(2,2′-dmglut)(H2O)]·2(H2O)}n (3), {[Cd(3,3′-azbpy)(glut)]·2.5(H2O)}n (4) and {[Co2(3,3′-azbpy)2(tp)(H2O)3]·H2O} (5), have been synthesized from 1,2-di(pyridine-3yl)diazene (3,3′-azbpy) using four different aliphatic and one aromatic dicarboxylic acid salt [succinate (suc2−), methyl succinate (msuc2−), 2,2′-dimethyl glutarate (2,2′-dmglut), glutarate (glut2−) and terephthalate (tp2−)] and two different transition metal salts by the slow diffusion technique at room temperature. The structures of the synthesized compounds 1–5 were characterized by single crystal X-ray diffraction analysis and by elemental analysis, infrared spectroscopy (IR), powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and UV–Vis spectroscopy. Compounds 1 and 2 show a honeycomb 3D structure, whereas, compound 3 exhibits a two-dimensional (2D) 2-fold interpenetrating network. Compound 4 shows a wavy 2D sheet structure and compound 5 exhibits a zero dimensional structure which forms a 2D sheet by means of hydrogen bonding, which by further π⋯π interactions forms an overall supramolecular 3D structure. Sorption studies with CO2 and N2 were also done for all the frameworks and a surface characteristic adsorption has been observed.

We synthesized a two-fold interpenetrated 3D MOF with two crystallographically distinct C[double bond, length as m-dash]C bonds, which undergoes [2+2] photo-cycloaddition and thermal reversible reaction, in a single-crystal-to-single-crystal (SCSC) manner. The softer nature and comparable mechanical properties of the crystals of the parent and cyclized MOFs revealed by nanoindentation allowed rationalizing their structural softness and SCSC transformation behaviour.

Highly symmetric enneanuclear copper(II) phosphates [Cu9(Pz)6(μ-OH)3(μ3-OH)(ArOPO3)4(DMF)3] (PzH = pyrazole, Ar = 2,6-(CHPh2)2-4-R-C6H2; R = Me, 2MeAr; Et, 2EtAr; iPr, 2iPrAr; and Ar = 2,6-iPr2C6H3, 2Dip) comprising nine copper(II) centers and pyrazole, hydroxide and DMF as ancillary ligands were synthesized by a reaction involving the arylphosphate monoester, 1, copper(I)chloride, pyrazole, and triethylamine in a 4 : 9 : 6 : 14 ratio. All four complexes were characterized by single crystal structural analysis. The complexes contain two distinct structural motifs within the multinuclear copper scaffold: a hexanuclear unit and a trinuclear unit. In the latter, the three Cu(II) centres are bridged by a μ3-OH. Each pair of Cu(II) centers in the trinuclear unit are bridged by a pyrazole ligand. The hexanuclear unit is made up of three dinuclear Cu(II) motifs where the two Cu(II) centres are bridged by an –OH and a pyrazole ligand. The three dinuclear units are connected to each other by phosphate ligands. The latter also aid the fusion of the trinuclear and the hexanuclear motifs. Magnetic studies reveal a strong antiferromagnetic exchange between the Cu(II) centres of the dinuclear units in the hexanuclear part and a strong spin frustration in the trinuclear part leading to a degenerate ground state.

Anion exchange materials are important for their application in toxic anion control process. Coordination Polymers (CPs) with weakly coordinated anions and lattice anions may be practically useful in anion exchange process. To explore this anion exchange properties by Coordination Polymers (CPs) we have synthesized two water insoluble cationic CPs {[Mn(bix)3(H2O)2].bix.(NO3)2}n (1), {[Cd(bix)2(NO3)2].(H2O)2}n (2) by using N,N-donors linkers bix {bix = 1,4-bis(imidazol-1-ylmethyl)- benzene}. Structure of complex 1 is 1D and contains lattice NO3– anion and the complex 2 is 2D and contains weakly coordinated NO3–anion. Both these complexes along with another previously published structurally similar CP {[Cd(bix)2(NO3)2]}n (3), response in anion exchange studies with foreign anions. All the anion exchange processes have been monitored by FT-IR spectroscopy and PXRD measurements.

Nanostructured conducting polymers are known to function as electroactive materials in sensor devices for adsorption and detection of different analytes. For the purpose of dopamine (DA) detection and CO2 gas adsorption we have prepared nanostructured polypyrrole (PPY) with the help of sodium cholate as surfactant. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) analyses and Brunauer–Emmett–Teller (BET) measurement have been done for the characterization of nanostructure and morphology of the prepared PPY. From the sorption measurement, it is observed that the rodlike PPY structures show highest N2 uptake (91.6 mL g−1) along with appreciable surface area (85.81 m2/g) and porosity (2.53 and 4.51 nm) values. It is also observed that the maximum uptake of CO2 is 173.885 mL g−1 at 195K for the PPY synthesized without any surfactant. Electrochemical characterization of PPY modified glassy carbon electrode (GCE) was done with impedance and cyclic voltammetry experiments. DA sensing in presence of ascorbic acid, uric acid and glucose was done by LSV technique. The PPY modified electrode exhibits sensitivity values of 0.301 and 0.19 μA μM−1 cm2 over two ranges of detection limits of 0.09–0.56 and 10–50 μM for dopamine, respectively (signal/noise = 3).

Syntheses, structural characterizations, photoluminescence, and adsorption properties of three new azo-functionalized Cd(II)-MOFs, namely, {[Cd(azbpy)(msuc)]·2.5(H2O)}n (2), {[Cd(azbpy)(mglu)]·5(H2O)}n (3), and {[Cd1.5(azbpy)2(glu)]·(NO3)·MeOH}n (4) [where msuc2- = methylsuccinate; mglut2- = methylglutarate; glut2- = glutarate; azbpy = 4,4'-azobispyridine] have been reported. The compounds show different structures only with the variation of aliphatic dicarboxylates. The photoswitching behavior for the above-mentioned newly synthesized Cd(II)-MOFs along with one of our previously reported other azo-functionalized Cd(II)-MOF, namely, {[Cd(azbpy)(suc)]·2(H2O)}n (1), has been studied extensively. At photoilluminated condition, the conductivity values can draw a clear structure-property relationship among the structures of compounds 1-4. Single crystal structural analysis reveals that all the compounds exhibit a three-dimensional (3D) framework connected by azbpy linker and respective aliphatic dicarboxylate through their bis-chelating mono/bis oxo-bridging fashion. Compounds 1-3 exhibit an iso-structural honeycomb like 3D framework showing the same coordination environments, where the metal-carboxylate 2D sheets of compounds 1-3 are pillared by N,N'-donor azbpy linkers. On the other hand, compound 4 exhibits a 2-fold interpenetrated 3D framework with a little difference in its coordination environment and the pillaring of 1D metal-carboxylate ladder by azbpy linkers. All the compounds significantly demonstrate their enhanced sensitivity under light rather than the dark condition. The gas and solvent vapor sorption studies have been performed for the synthesized compounds 2-4. Moreover, compound 2 exhibits an enhanced type IV selective CO2 adsorption isotherm over N2 along with the appearance of gate opening phenomena in that.

Three different N,N′-donor ligands with Zn(NO3)2·6H2O and two different dicarboxylates, flexible succinate (suc) and rigid fumarate (fum) afforded six different metal–organic frameworks (MOFs). Among the N,N′-donor ligands, one bent 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene (3-bpdb) gives two isostructural two-dimensional MOFs, {[Zn(3-bpdb)(suc)]·(H2O)2}n (1) and {[Zn(3-bpdb)(fum)(H2O)2]}n (2). The use of a straight N,N′-donor ligand, i.e., 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene (4-bpdb), results in two three-dimensional (3D) MOFs, {[Zn4(4-bpdb)2(suc)3(OH)2]·5(H2O)}n (3) and {[Zn(4-bpdb)(fum)]·(H2O)2}n (4). Here, 3 is a pillared layer structure, whereas 4 has a 5-fold interpenetrated dimondoid network. For both the bent and straight N,N′-donor ligands an imine alike motif is embedded in the structure. When this motif is replaced by a C–C double bond by using the ligand 1,2-bis(4-pyridyl)ethylene (bpee), it produces two MOFs, {[Zn(bpee)(suc)]2·(H2O)3}n (5) and {[Zn2(bpee)2(fum)2]·(H2O)}n (6), having a...

A novel benzimidazole appended arylimide (pyromellitic, naphthalene and perylene) based covalent organic framework (COF) has been synthesized through the condensation polymerization pathway, by taking consideration of the special noncovalent interaction with carbon dioxide. Formation and chemical connectivities of these polymers were thoroughly investigated by 13 C NMR and FTIR studies. Presences of pores in these polymers have been primarily checked with FESEM and HRTEM observations, prior to adsorption studies. The pyromellitic diimide containing benzimidazole COF (BIBDZ) exhibit highest BET surface area, 177.095 m 2 g −1 with pore diameter of 30–32 angstorm among the COFs reported here which is also consistent with our computational study. Naphthalene diimide and the diaminobenzidine containing COF (NIBDZ) has the highest binding affinity with CO 2 i.e. 127.87 cc g −1 (14.56 wt%) at 195 K, than the other two COFs. On the other side BIBDZ has showed specific capacitance value of 88.4 F g −1 at 0.5 A g −1 current density in the 1M H 3 PO 4 electrolytic solution as well as remarkable retention of specific capacitance (93.61%) after 5000 galvanostatic charge discharge cycles.

Because of their potential applications, coordination polymers (CPs) are at an exalted position in the field of chemical and material science. Porous coordination polymers, popularly known as metal–organic frameworks (MOFs), have large surface area with functional pore environment, permanent porosity, tailorability in pore size, dimension and volume, which make them promising for interesting functionalities. In this review, we show how the mixed-ligand CPs/MOFs are very important in tuning the functionality of such systems and how the X-ray structure illuminates their functionalities. Here, we discuss the application of mixed-ligand functional MOFs for CO2 storage and separation by fine-tuning their pore size and dimension along with their polar pore surfaces using different functional dicarboxylates and N,N′-donor ligands. We also discuss the nature of conductivity and fabrication of Schottky barrier diode for CPs, where free organic ligands are in their pores. In addition, we also present the variation of their interesting chemical reactivity, e.g. framework-assisted in situ redox transformation.

Five sulfonic acid group functionalized mixed ligand coordination polymers (CPs), namely, {[Zn(bpeH)(5-sip)(H2O)]·(H2O)}n (1), {[Cu(pyz)(5-Hsip)(H2O)2]·(H2O)2}n (2), {[Cu(bpee)0.5(5-sip)(H2O)2]·(H2O)4(bpeeH2)0.5}n (3), {[Cu(bpy)(5-Hsip)(H2O)]·(H2O)2}n (4), and {[Cu(bpy)2(5-H2sip)2]·(H2O)6}n (5) [where sip3– = 5-sulfoisophthalate; bpe = 4,4′-bispyridylethane; pyz = pyrazine; bpee = 4,4′-bispyridylethylene; bpy = 4,4′-bipyridine], have been synthesized with varying different N,N′-donor linkers using slow diffusion techniques at room temperature. The CPs possess guest water filled 1D channels and noncoordinating sulfonic acid or coordinated sulfonate groups, which are interconnected by means of extended intermolecular H-bonding interaction, which supports the humidity dependent proton conductivity of the samples. Under 95% relative humidity (% RH), the CPs exhibit the temperature dependent proton conductivity which is maximum up to in the range of ∼10–5–10–6 S cm–1 at 65 °C. In most of the cases, the framewo...

Two new mixed ligand coordination polymers (CPs) that are sulfonic group functionalized, namely, {[Cd(bpe)0.5(5-sip)(H2O)]·4H2O(bpeH2)0.5}n (1) and {[Cd1.5(bte)(5-sip)(H2O)3]·3H2O}n (2) [where 5-si...

A pair of supramolecular isomers of CdII -based MOF have been synthesized by utilizing a flexible N,N'-donor linker and a dicarboxylate with ESIPT (excited-state intramolecular proton transfer) fluorophore by varying the reaction media. One of the MOFs has a 3D four-fold interpenetrating framework with guest solvent in the structure that undergoes a solvent-dependent crystalline-to-crystalline structural transformation, which has been extensively studied by powder XRD and IR spectroscopy. The other MOF is structurally rigid in nature and has a two-fold interpenetrating structure without any guest molecules. Both the compounds show moderate CO2 adsorption and one of them, the MOF with the four-fold interpenetrating structure, also shows moderately high H2 adsorption. Furthermore, both the compounds show interesting luminescence behavior. In the solid state, the two compounds show single-peak spectra, whereas upon suspension of these compounds in polar solvents, the maxima split into two peaks with a large Stokes shift. On the other hand, in nonpolar solvents, only one emission maximum is observed. This solvatochromic dual-emission phenomenon is due to ESIPT, which has been extensively studied.

A 2D + 2D → 3D inclined polycatenated dynamic metal–organic framework of {[Cu(4-bpe)(2-ntp)(H2O)2]·2H2O}n [1, where 2-ntp2– = 2-nitroterephthalate and 4-bpe = 1,2-bis-(4-pyridyl)ethane] has been synthesized and characterized. The variable-temperature powder X-ray diffraction study indicates the dynamic nature of the inclined polycatenated framework, and the dehydrated framework with exposed metal centers exhibits excellent type I H2 adsorption of 1.94 wt % at 77 K and 1 bar of pressure.

Assembly of diphenylphosphate (dpp) with Cu(II) salts in combination with the different N-donor linkers, e.g., pentamethyldiethylenetriamine (pmdeta), bis-(3-aminopropyl)amine (bapa) and 4-Picolene (4-pic), yielded three new metal-organic coordination complexes, namely {[Cu(dpp)(pmdeta)] ⋅ClO4.H2O}2 (1), {[{[Cu(dpp)(bapa)H2O] ⋅ClO4} (2) and [Cu(dpp)2(4-pic)2]2 (3) by stirring the constituent reactants at room temperature. Complexes 1–3 were characterized by single crystal X-ray diffraction analysis and were further characterized by elemental analysis, infrared spectroscopy (IR) and powder X-ray diffraction (PXRD) studies. Compound 1 exhibits a dimeric Cu(II) complex which forms a 1D supramolecular chain along the crystallographic c-axis by means of intermolecular π…π interactions. Compounds 2 and 3 form a monomeric and dimeric complex of Cu(II) respectively, which are further extended into a supramolecular 2D structure via C-H.. π interactions for 2 and a 3D structure for 3 with the help of both intermolecular C-H.. π and π…π interactions for 3. In addition, the solid state UV-Vis spectra of compounds 1-3 and free dpp ligand have been investigated at room temperature.

A family of dicyanamide bridged compounds namely {[Co(dca)4(2-abim)2]}n (1), {[Ni(dca)4(2-abim)2]}n (2), {[Cd(dca)4(2-abim)2]}n (3), {[Zn(N(CN)2)2(4-bpdb)]}n (4) and {[Cd(N(CN)2)2(4-bpdb)]}n (5); [where dca = dicyanamide, 2-abim = 2-aminobenzimidazole and 4-bpdb = 1,4-bis-(4-pyridyl)-2,3-diaza-1,3-butadiene] have been synthesized by stirring at room temperature. These compounds have been characterized by single crystal diffraction analysis, infrared spectroscopy (IR) and powder X-ray diffraction (PXRD). Complexes 1–3 are isostructural and exhibit two-dimensional (2D) metal-dca sheet with pendant 2-abim ligand. Compound 4 forms [Zn(N(CN)2)]n chains with a pendent dca and a bridging dca linker, which are further connected by bridging 4-bpdb ligands extending into a 2D layer structure. In case of compound 5 each Cd(II) centers connect with four bridging dca linkers to form [Cd(N(CN)2)]n double chains, which are further connected by bridging 4-bpdb ligands extending into a 2D layer structure. Here [Cd2(N(CN)2)] and 4-bpdb spacer are interpenetrated to each other and resemble polyrotaxane-type structures. Photoluminescent properties of compounds 3–5 were also studied and they exhibit nice ligands based photoluminescence properties at room temperature.

A guest-dependent dynamic fivefold interpenetrated 3D porous metal-organic framework (MOF) of ZnII ions has been synthesized that exhibits selective carbon dioxide adsorption. Furthermore, the MOF shows excellent luminescence behavior, which is supported by a systematic study on the guest-responsive multicolor emission of a suspension of the MOF. The dual-emission behavior arises from the excited-state intramolecular proton transfer (ESIPT), and the compound also shows remarkable potential to detect traces of water in various organic solvents. The experimental observations were also painstakingly authenticated by using time-dependent density-functional-theory (DFT) calculations.

Three new dynamic metal–organic frameworks (MOFs) namely {[Cd2(3,4-pyrdc)2(4,4′-bipy)(H2O)2]·4H2O}n (1), {[Mn2(3,4-pyrdc)2(bpee)(H2O)2]·H2O}n (2), and {[Cu2(3,4- pyrdc)2(bpp)2(H2O)4]·5H2O}n (3), based on 3,4-pyridinedicarboxylate (3,4-pyrdc) and three different N,N′-donor ligands [4,4′-bipyridine (4,4′-bipy), 1,2-bis(4-pyridyl)ethylene (bpee), and 1,3-bis(4-pyridyl)-propane (bpp)] with various divalent transition metal ions have been synthesized and characterized by single-crystal and powder X-ray diffraction and other physicochemical methods. In compounds 1 and 2, the 3,4-pyrdc ligand forms two-dimensional (2D) metal–carboxylate sheets that are connected by N,N′-donor ligands to form three-dimensional (3D) structures with water-filled channels. In compound 3, the 3,4-pyrdc ligand affords one-dimensional metal–carboxylate chains. These chains are connected by the more flexible bpp ligand to form 2D structures, which are extended to a 3D supramolecular architecture by H-bonding. Compounds 1 and 2 show a re...

Five azo-functionalized coordination polymers (CPs), namely, [Zn(azbpy)(NO2-bdc)·H2O]n (1), [Zn(azbpy)(NO2-bdc)]n·3H2O (2), {[Cd(azbpy)(NO2-bdc)·H2O]·2H2O}n (3), {[Mn(azbpy)2(NO2-bdc)]2}n (4), and {[Co(azbpy)(NO2-bdc)(H2O)2][Co(azbpy)0.5(NO2-bdc)(H2O)3]}n (5) have been synthesized using different transition metal salts with 5-nitro-1,3-benzenedicarboxylate (NO2-bdc2–) and 4,4′-azobispyridine (azbpy) ligand using a slow diffusion technique at room temperature. The complexes 1–5 were characterized by single crystal X-ray diffraction analysis, elemental analysis, infrared spectroscopy (IR), powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA). In the solid state, compound 1 shows a wavy one-dimensional (1D) ladder; constructed through the N,N′-donor azbpy and NO2-bdc2– ligands with the metal centers, whereas compound 2 exhibits a bilayer two-dimensional (2D) sheet containing a wavy 1D ladder of metal-carboxylate, and compound 3 shows a stairlike wavy 2D sheet. Compound 4 exhibits a novel 2-f...

Two nitro functionalized Cu(II)-MOFs exhibit high CO2 uptake with nice selectivity over other gases like H2, N2, and CH4, which is potentially important for the removal of carbon dioxide from industrial flue gas and natural gas. Here the selective CO2 adsorption by these MOFs is primarily due to the presence of suitable voids with −NO2 group functionalized pore walls in the dehydrated framework, which is unprecedented.

Two metal–organic frameworks of Cd(II) from 3,4-pyridinedicarboxylate (3,4-pyrdc) and 1,2-bis(4-pyridyl)ethane (bpe) ligands, {[Cd(3,4-pyrdc)(bpe)(CH3OH)]·(H2O)}n (1) and {[Cd(3,4-pyrdc)(bpe)0.5(H2O)]·(H2O)}n (2) have been synthesized by changing the reaction medium. Compound 1 exhibited a 2D structure while compound 2 showed a 3D structure, which have both been revealed by single crystal X-ray studies. Both of the compounds showed interesting solvent mediated reversible structural transformations which have been established by exhaustive X-ray powder diffraction studies, elemental analysis, IR spectroscopy and thermogravimetric analysis. The desolvated form of the 2D framework (1) undergoes an irreversible structural transformation to form the 3D framework (2) upon soaking with water. The 2D to 3D transformation occurs through precise bond rotation and bond breaking which has been established by a GC–MS study. Sorption experiments with different gases and volatiles were performed for both the metal–organic frameworks and clearly indicated the differences in their inherent flexibility and transformability.

Two new mixed ligand metal–organic frameworks of Zn(II) with disodium 5-hydroxyisophthalate and 4,4′-azobispyridine (azbpy) ligands, {[Zn(azbpy)(HO-1,3-bdc)(H2O)]·(azbpy)}n (1) and {[Zn(azbpy)0.5(HO-1,3-bdc)(C2H5OH)]·(H2O)}n (2) have been synthesized by changing the reaction medium (methanol to ethanol) and structurally characterized by elemental analysis, IR, PXRD, TG and single crystal X-ray diffraction. Compound 1 exhibits a 2D sheet network structure with free azbpy ligands in its void space, and is stabilized by π–π and C–H⋯π interactions, whereas 2 has a 2D layered architecture with lattice water molecules in its void space. Compound 2 has a flexible structure and shows gated adsorption (gas and solvent) behavior, while framework 1 is nonporous. These two MOFs exhibit remarkable electrical conductivity values at room temperature and their comparison is discussed carefully. Theoretical calculations suggest that both the compounds are p-type semiconductors and correlate the structure–property relationship. Schottky barrier diode electronic devices have been fabricated by using these two semiconductor materials with aluminium (Al) and indium tin oxide (ITO) in sandwich configuration, ITO/MOF-1 or 2/Al, and both the devices exhibit sound rectification behavior. The photoluminescent properties of both the compounds in the solid state are also investigated in detail.

Solar photovoltaic (SPV) cells have become ubiquitous in meeting the increasing global energy demand, but they face major challenge of performance degradation due to dust on the SPV panels. The traditional mechanical methods of cleaning are costly and time consuming. To ameliorate this problem, a “self-cleaning” superhydrophobic coating is laid on the upper glass cover of SPV array that repels water. This promotes droplet roll-off, enabling a very small amount of water to clean the surface. Herein, such a coating on glass has been developed by depositing 10–20 nm silica nanoparticles via a facile sol–gel method on glass surface and grafting a layer of fluoroalkylsilane above it. Surface roughness, wettability and durability of the fabricated coating are characterized through surface profiling, contact angle measurements and droplet impact test, respectively. The treated surface shows an attenuation of 6 ± 1.24% of the incident radiation, while the SPV voltage output is only slightly affected. Moreover, the treated surfaces show significantly better recovery in the SPV-cell performance upon cleansing with a measured quantity of water than that observed with the untreated surface.

Post synthetic modification of coordination polymers have been extensively studied through years, to obtain several marvelous functional materials. Apart from the usual metal or ligand exchange, irreversible structural transformation strategy may also be a useful approach to perform post synthetic modification in coordination polymers for creating functional materials. Considering this approach, three coordination polymer of Zn(II) and Co(II) namely, {[Zn(beb)(dmglut)]}n (1), {Co2(beb)2(hipt)2(H2O)1.5(MeOH)}]n (2) and {[Zn2(beb)2(fum)2]}n (3) (Whereas beb = 1-(2-(1H-benzoimidazol-1-yl)ethyl)-1H-benzoimidazole, dmglut = 3,3′-dimethylglutarate, hipt = 5-hydroxyisophthalate and fum = fumarate) have been synthesized from flexible beb ligand and three different dicarboxylates. Compound 1 and 2 are with a two dimensional structure which are adjoined by weak forces to form a supramolecular three dimensional architecture. Compound 3 has a three dimensional structure with unidirectional channels. Compound 2 and 3 have undergone irreversible structural transformation. These transformations are thoroughly monitored by PXRD analysis, UV–vis spectroscopy, and IR spectroscopy. Solid state emission spectral analyses for two Zn(II) CPs and gas sorption analyses for all the compounds has been also performed.

Three new coordination complexes [Mn(L1)(μ-azide)(azide)]2⋅4H2O (1), [Mn(L1)(fum)]n (2) [L1 = 2methyl-N1,N2-bis(pyridin-2yl)propane-1,2-diamine, fum = Fumaric acid] and [Co(L2)(azide)] (3) [L2 = 6 phenyl-1,3,5-triazine 2,4-diyl amino(pyridine-2yl)methanol] have been synthesized and X-ray crystallographically characterized. Complex 1, a dinuclear Mn(II) complex is formed by bridging azide ligand and other coordination sites are satisfied by tetradentate ligand L1 and terminal azide ligand. The overall structure is an incomplete supramolecular 3D cage structure, formed by intermolecular π … π interaction of pyridyl ligand and hydrogen bonding. Complex 2 comprised of eight coordinated Mn(II) centre where ligand L1 and fumarate is bridged between the metal centers that leads to a one dimensional chain structure which further extended to a 3D structure by π … π and C–H … π interactions. The overall structure is further stabilized by hydrogen bonding with the guest water molecules. Complex 3, a six coordinated mononuclear Co(II) discrete complex is consist of pentadentate ligand L2 and azide act as a terminal ligand. This Mononuclear complex is connected by π … π, C–H … π interactions and hydrogen bonding which ultimately leads to a supramolecular 2D architecture. All the complexes have been further characterized by elemental analysis, infrared spectroscopy (IR) and powder X-ray diffraction (PXRD) studies.

Assembly of 5-nitroisophthalate (nip2−) with first row transition metal salts [Mn(II), Fe(II), Co(II), Zn(II)] in combination with the various neutral auxiliary N,N′-donor linkers, e.g., 2,5-bis-(4-pyridyl)-3,4-diaza-2,4-hexadiene (4-bpdh), 1,3-bis(4-pyridyl)propane (bpp) and 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene (4-bpdb), yielded eight new coordination polymers (CPs), namely {[Mn(4-bpdh)(nip)(H2O)2]·H2O}n (1), {[Fe(4-bpdh)(nip)(H2O)2]·H2O}n (2), {[Co(4-bpdh)(nip)(H2O)2]·H2O}n (3), {[Mn2(bpp)2(nip)2(H2O)2]·H2O}n (4), {[Fe(bpp)(nip)(H2O)]·H2O}n (5), [Zn(bpp)(nip)(H2O)]n (6), {[Fe(4-bpdh)1.5(nip)]·(4-bpdh)0.5}n (7) and {[Fe(4-bpdb)(nip)]·(4-bpdb)0.5(H2O)}n (8) using the slow diffusion technique at room temperature. The complexes 1–8 were characterized by single crystal X-ray diffraction analysis and were further characterized by elemental analysis, infrared spectroscopy (IR) and powder X-ray diffraction (PXRD). Complexes 1–3 are isostructural and exhibit a one-dimensional (1D) metal-carboxylate chain with pendant 4-bpdh ligands, which is further extended into a three-dimensional supramolecular structure by means of H-bonding and π–π interactions. Complexes 4–6 are also isomorphous, but distinctly different from the first three complexes. They exhibit a similar 2-fold interpenetrated three-dimensional (3D) net with 66 dia net topology. Compound 7 displays a two-dimensional (2D) grid-like structure, having 4-bpdh ligands in the crystal void, and this is further extended by means of intermolecular π–π interactions into a 3D supramolecular structure, whereas compound 8 possesses a different 2D grid structure containing free 4-bpdb ligands in the void spaces. The thermal stabilities and UV–Vis spectra of all the complexes and the luminescent properties of complex 6 were also studied.

Single crystal X-ray diffraction of two macrocyclic bischalcones, namely, (2E,25E)-11,17,33,37-tetraoxapentacyclo[36.4.0.05,10.018,23.027,32]dotetraconta-1(42),2,5,7,9,18,20,22,25,27,29,31,38,40-tetradecaene-4,24-dione(1) and (2E,24E)-11,16,32,37-tetraoxapentacyclo[36.4.0.05,10.017,22.026,31]dotetraconta-1(42),2,5,7,9,17,19,21,24,26,28,30,38,40-tetradecaene-4,23-dione(2), each containing a 26-membered ring, has been studied. Compound 1 belongs to the monoclinic system, space group C2/c with a = 34.3615(9) Å, b = 12.7995(3) Å, c = 14.6231(3) Å, β = 96.912(2)°, V = 6,384.6(3) Å3, and Z = 8. Compound 2 is triclinic, space group P-1 with a = 10.066(2) Å, b = 10.670(3) Å, c = 16.590(3) Å, α = 85.95(2), β = 89.244(14), γ = 62.211(13), V = 1572.0(6) Å3, and Z = 2. Intermolecular C–H⋯O hydrogen bonding interactions are present in both compounds.

Seven coordination polymers (CPs) with two types of framework structures, namely, {[M(4-bpdb)(1,3-bdc)]·(4-bpdb)0.5}n [M = Mn (1), Fe (2), and Co (3)], and {[M(4-bpdh)(1,4-bdc)]}n (M = Mn (4), Fe (5), Co (6), and Cd (7)] have been synthesized through the slow diffusion technique using 1,3-bdc and 1,4-bdc ligands with two different azine based N,N′-donor linkers [1,3-bdc = benzene-1,3-dicarboxylate, 1,4-bdc = benzene-1,4-dicarboxylate, 4-bpdb = N,N′-bis-pyridin-4-ylmethylene-hydrazine and 4-bpdh = N,N′-bis-(1-pyridin-4-yl-ethylidene)-hydrazine]. Their structures have been determined by single-crystal X-ray diffraction analysis and further characterized by elemental analysis, IR spectra, and powder X-ray diffraction (PXRD) analysis. Compounds 1–3 are isostructural and feature a two-dimensional (2D) framework structure formed by pillaring the one-dimensional [M(1,3-bdc)]n double chains through 4-bpdb linkers. In all cases of compounds 1–3, free 4-bpdb linkers are present in the lattice and lattice 4-bpdb lig...

Porous coordination polymers (PCPs), also referred to as metal–organic frameworks (MOFs), have firmly established themselves as a class of excellent solid-state sorbents for carbon dioxide (CO2) along with their other several exciting properties. The mixed-ligand PCPs, constructed with polycarboxylates and N,N′-donor ligands, have been adopted for the fabrication of novel functional PCPs/MOFs, as the combination of different ligands with metal ions offer a better control over the structural variation of the frameworks compared to a single ligand. In this highlight, we have emphasized some of such important mixed linker-based MOFs with different carboxylate ligands and N,N′-donor linkers that act as excellent materials for CO2 adsorption and separation. The prospect of such mixed-ligand MOFs for the effective separation and sequestration of CO2 is also addressed by means of discussing different strategies for designing mixed-ligand MOFs that not only can potentially improve the amount of CO2 adsorption but also can increase the selectivity of CO2 uptake over other gases and volatiles.

Two new isostructural porous coordination polymers of Zn(II) {[Zn2(NH2-bdc)2(4-bpdb)]·(H2O)4}n (1) and {[Zn2(NH2-bdc)2(4-bpdh)]·(H2O)4}n (2) [4-bpdb = 1,4-bis-(4-pyridyl)-2,3-diaza-1,3-butadiene, 4-bpdh = 2,5-bis-(4-pyridyl)-3,4-diaza-2,4-hexadiene and NH2-bdc = 5-amino-1,3-benzenedicarboxylate] have been synthesized using a mixed ligand system by solvent diffusion and structurally characterized through single crystal X-ray diffraction, variable temperature powder X-ray diffraction and thermogravimetric analysis. Both the coordination polymers are constructed using linear Schiff base linkers of similar length having N–N base functionalities but the only difference is the presence of methyl groups in adjacent carbon atoms of the N–N group in the 4-bpdh ligand. Single-crystal structure analysis revealed that both compounds 1 and 2 have two-dimensional (2D) pillared-bilayer framework structures containing 1D channels (8.3 × 3.8 A2 for 1 and 8.0 × 1.6 A2 for 2) filled with lattice water molecules. Channel dimensions in 2 decrease due to the presence of methyl groups. The desolvated frameworks of 1 and 2 are rigid which is evidenced by variable temperature PXRD. Both the compounds show type-I CO2 uptake profiles and the differences in CO2 adsorption uptakes have been corroborated to their void space (27.1% for 1 and 17.1% for 2). Desolvated forms of compound 1 exhibit remarkably high water adsorption capacity even at low vapor pressure whereas desolvated forms of compound 2 show very low water vapor uptake, which could be ascribed to the hydrophobic nature of the pore surface of 2.

Tailor made synthesis of the azoaromatics, HL 1 –HL 2 [HL = 2-(arylamino)phenylazopyridine] containing ionophoric crown moiety is described. Coordination induced C–N bond fusion synthetic protocol was successfully implemented for the synthesis of these compounds that are subsequently characterized using various spectroscopic techniques. Single crystal X-ray structures of the cobalt compounds, [ 1a ] + and [ 1b ] + , clearly characterize the ionophoric ligand and its tridentate coordination mode via deprotonation of the secondary amine proton. Moreover, the structural analysis of [ 1b ] + reveals the receptor ability of benzo-15-crown-5 towards alkali metal ion in solid state. This complex shows two O…π contact, which resulted in the formation of a helical 1D supramolecular chain. Electrochemical studies exhibit anodic shift of the reduction potentials of the Co III center in the presence of Na + thereby indicating complexation of these ions to the crown moiety.

Two new Cd(II) coordination polymers, namely [Cd(3-bpdh)2(ClO4)2]n (1) and {[Cd(3-bpdh)(suc)(H2O)]·3(H2O)}n (2), have been synthesized using a substituted bent N,N'-donor ligand 2,5-bis-(3-pyridyl)-3,4-diaza-2,4-hexadiene (3-bpdh) and aliphatic dicarboxylate disodium succinate (suc) with Cd(II) perchlorate salts at room temperature by a slow diffusion technique for the exploration of our previous reported work. Both the structures were determined by single-crystal X-ray diffraction analysis and also by other physicochemical methods. Structure analysis revealed that complex 1 is a 1D chain structure containing coordinated perchlorate with a metal centre, and complex 2 shows a porous 3D framework with encapsulation of lattice water molecules into the void along the crystallographic a-axis. The PXRD study shows the bulk purity of both the complexes and TGA analysis of 2 exhibits that the structure is thermally stable up to 250 °C. Complex 1 shows a nice anion exchange property with replacement of weakly coordinated perchlorate with the inclusion of new anions; and the anion exchanged solids were characterised by FT-IR, PXRD and photoluminescence properties. The desolvated framework of 2 exhibits sorption of CO2 and water vapor and surface adsorption of N2 corroborating with the nature of the pore environment present in 2. The photoluminescence study has been also done for both complexes in the solid state which exhibits ligand based emissions at room temperature.

Syntheses, structural characterizations, photoluminescence, and adsorption properties of three new azo-functionalized Cd(II)-MOFs, namely, {[Cd(azbpy)(msuc)]·2.5(H

Figure. In two new complexes of Mn(II) and Zn(II), it has been observed that carboxylate (O)…π interactions played a crucial role in the organization of supramolecular structure and that carboxylate (O)…π interactions also somehow controlled by the C-H…π interactions, which is achieved by proper modulation of the linkers.

Reactions with an aliphatic dicarboxylate (oxalate) as well as an aromatic dicarboxylate (terepthalate) in combination with an N,N′ donor ligand (trans-4,4′-azobispyridine) results two new coordination polymer of divalent manganese, namely {[Mn(azbpy)(H2O)4]·(bdc)·(H2O)2}n, (1) and {[Mn(ox)(H2O)2]·(azbpy)·(H2O)2}n,(2). Both the coordination polymers have one dimensional structure and extended to two-dimension by means of H-bonding. Interestingly, in solid state structure, the hydrogen bonding interaction recognizes the dicarboxylate (bdc) in case of 1 and N donor ligands (azbpy) in 2. The variation in the use of dicarboxylates, creates here a huge variation in the co-ordination modes of the metal ion as well as in the supramolecular structure within the crystal of 1 and 2. The contribution of various types of non-covalent forces are quantitatively explained in the light of Hrishfield surface analysis, which justifies the role of hydrogen bonding in the recognition of the above organic linkers. A DFT calculation of NBO also gives a quantitative understanding of the formation of the solid state structure by H-bonding. A thermogravimetric analysis, solid state fluorescence spectra and EPR spectroscopic study of the complexes have also performed which also nicely corroborated their crystal structures.

Two isostructural coordination polymers based on Co(II) and Ni(II), {[M(azpy)3(p-bdc)2(H2O)4]·(CH3OH)2(H2O)3}n [where M = Co (1) and Ni (2); azpy = N,N′-bis-pyridin-4-ylmethylene-hydrazine and p-bdc = 1,4-benzenedicarboxylate], have been synthesized using mixed ligand systems at room temperature and characterized by single-crystal X-ray diffraction and other physicochemical methods. Structure determination reveals that both the complexes crystallize in the monoclinic space group C2/c and exhibit one-dimensional (1D) ladder like structures constructed by p-bdc and azpy ligands in which Schiff base (azpy) linkers serve as a bridging as well as pendent ligands. These pendent ligands are involved in H-bonding and π–π interactions with lattice water, methanol molecules and bridging azpy ligands, to form the 3D supramolecular structure. Notably, both the frameworks efficiently catalyze the Knoevenagel condensation reactions of a wide range of substituted benzaldehydes with active methylene compounds in heterogeneous medium under environmentally friendly conditions and the products were obtained in excellent yields. These catalysts were also found to exhibit excellent recyclability and re-usability without any significant loss of activity. A variable temperature magnetic study of both compounds was carried out and their magnetic properties justified on the basis of their crystal structure.

Five new mixed ligand coordination polymers, {[Co0.5(H2O)(1,4-bdc)(3-bpdb)Co0.5(H2O)2]·(H2O)3}n (1), [Co(3-bpdh)(1,4-bdc)(H2O)2]n (2), [Zn(3-bpdb)(1,4-bdc)]n (3), {[Zn(3-bpdh)(1,4-bdc)]·(3-bpdh)0.5}n (4) and [Cd(3-bpdb)(1,4-bdc)(H2O)]n (5) [where 3-bpdb = 1,4-bis-(3-pyridyl)-2,3-diaza-1,3-butadiene; 3-bpdh = 2,5-bis-(3-pyridyl)-3,4-diaza-2,4-hexadiene and 1,4-bdc = benzene-1,4-dicarboxylate] were synthesized at room temperature. The structures of 1–5 were determined by single crystal X-ray diffraction analysis and were further characterized by elemental analysis, infrared spectroscopy (IR) and powder X-ray diffraction (PXRD). Compound 1 exhibits a one-dimensional (1D) chain structure with monodentate pendant 1,4-bdc ligands which further extend to a three-dimensional (3D) supramolecular structure by H-bonding and π⋯π interactions. Compound 2 displays a 4-connected two-dimensional (2D) framework with the point symbol {44·62}. Moreover, the 2D structure of 2 is also ultimately packed into 3D supramolecular frameworks through H-bonding and π–π stacking interactions. Compound 3 shows a 5-fold interpenetrated diamondoid net with 66 topology. Compound 4 is a 2D 3-connected net having a point symbol {63} and is extended to a supramolecular 3D structure through C–H⋯π and π⋯π interactions with lattice 3-bpdh ligands. Compound 5 features a 3-fold interpenetrated diamondoid net with 66 topology. The thermal stabilities and luminescent properties of 3–5 were also studied in detail. The complexes exhibit ligands based photoluminescence properties at room temperature.

We report the synthesis, structural characterization and adsorption properties of three new porous coordination polymers {[Cu(Meazpy)0.5(glut)](H2O)}n (2), {[Zn(azpy)0.5(terep)](H2O)}n (3), and {[Zn(Meazpy)0.5(terep)]}n (4) [glut = glutarate, terep = terephthalate, azpy = N,N'-bis-(pyridin-4-ylmethylene)hydrazine and Meazpy = N,N'-bis-(1-pyridin-4-ylethylidene)hydrazine] composed of mixed linkers systems. Structure determination reveals that all three compounds have three-dimensional (3D) coordination frameworks bridged by dicarboxylates and Schiff base linkers. In all cases 2D dicarboxylate layers are supported by paddle-wheel M2(CO2)4 SBUs extended in three dimensions by designed Schiff base linkers. Compound 1, which has been reported in a paper earlier by our group, is a robust porous three-dimensional (3D) framework whose pore surface was found to be decorated with the -CH=N- groups of a linear Schiff base (azpy) and it showed reversible single-crystal-to-single-crystal transformation and selective CO2 uptake. By using another linear Schiff base linker Meazpy, we have synthesized compound 2 which is isostructural with 1, having an additional methyl group pointing towards the pore. Like 1 it also shows a reversible single-crystal-to-single-crystal transformation upon dehydration and rehydration. The dehydrated framework of 2 exhibits 50% enhanced CO2 uptake compared to 1. This has been achieved by the pore surface modification effected upon changing the pillar backbone from a -CH=N- to -CMe=N- group. It also adsorbs water vapour at 298 K. In the case of the two isostructural 3D MOFs 3and 4, the use of a rigid carboxylate (terephthalate) linker arrested porosity by three-fold interpenetration. We showed that the use of aliphatic dicarboxylate (glutarate) results in a non-interpenetrated framework rather than the common interpenetrated framework with aromatic dicarboxylates in mixed ligand systems.